There has been a demand for further reduction of NOx in gas turbine exhaust gas from the standpoint of environmental protection. The premixed combustion where the fuel and air are premixed before combustion is known as a combustion method for gas turbine combustor. This method enables significant NOx reduction as compared with diffusion combustion where a fuel is directly sprayed and combusted in a combustion chamber.
Therefore, an increasing number of gas turbines have adopted the premixed combustion to meet the recent NOx emission control standard.
JP 2009-14297 discloses a gas turbine combustor which includes a fuel nozzle for forming a coaxial jet stream of fuel and air, and a fuel nozzle header. JP 2009-14297 also discloses a structure to achieve a longer service life by suppressing heat stress generated in the fuel nozzle header. Specifically, the fuel nozzle header includes a mounting hole for mounting the fuel nozzle. In the mounting hole of the fuel nozzle header, a space section for air layer or a hollow-cylindrical shaped heat-insulating layer is formed between an outer periphery of the fuel nozzle and an inner periphery of the mounting hole. A tail end of the fuel nozzle is provided with engagement means for engagement with the mounting hole of the fuel nozzle header or an end face of the fuel nozzle header formed with this mounting hole. The fuel nozzle is fixed to the fuel nozzle header via the engagement means.
The premixed combustion where the fuel and air are premixed before combustion is known as a measure for reduction of NOx emissions from the gas turbine combustor. However, the premixed combustion is more likely to encounter combustion oscillation than the diffusion combustion where the fuel is combusted after directly sprayed into the combustion chamber. The premixed combustion involves fear that combustor components such as the fuel nozzle are subjected to oscillation stress, sustaining damages caused by high-cycle fatigue.
JP 2009-14297 makes no mention of measures against the fear that the combustor components such as the fuel nozzle are subjected to oscillation stress and sustain damages caused by high-cycle fatigue.
In view of the above problems, the present invention is directed to a premixing fuel nozzle for gas turbine combustor which can even adopt the premixed combustion where the fuel and air are premixed before combustion. The invention has an object to provide a fuel nozzle for gas turbine combustor which increases oscillation strength and eliminates fear of damaging any combustor component by being prevented from scattering in a downstream direction in the event of breakage of the fuel nozzle at a welded part between the fuel nozzle and an end flange.